While it may be the case that many Christians see things as you describe, that isn't really what Christianity teaches. I am Christian and I would not say that God is the good force of the universe and Satan is the evil force in the universe doing battly by proxy on earth. Not at all. Neither would my teachers, who happened to be priests. Furthermore, Christians do recognize destruction as part of the natural order of things. At least, on the physical level. All things made of matter change, and destruction is a nessecary part of that change, since as soon as a thing changes, what it was before is no longer, and something new is in its place. There is a certain seed (akin to the pinecone, but I'm not sure of the name of the tree), which only opens under the heat of fire. The only way for this tree to spread its seed is out of the flames of a forest fire. Destruction brings about creation. This is how it is in the physical world. But it is not thus in the spiritual.
I think this is where a lot of the confusion comes in. Good and evil are seen as positives and negatives. By this, I do not mean to draw parallel to a magnet, but I mean that one posits (adds, grows... or simply is, ect..) and one negates (removes from, destroys.... or lacks, etc..). But from what? Nature. A thing is only said to be evil if it negates or destroys the nature of a thing. There is definitely destruction within the natural world, but it is when the nature of the natural is distorted or destroyed that we call it evil. I don't doubt that if someone saw a cat walking down the street with one leg missing its ears all torn up that person would not be saddened or consider it a wrong. The cat will die eventually, yes, that is part of its nature. However, it is not natural for a cat to have only three legs and missing part of its ears. Isn't it also true that factory farms are a terrible wrong, and people are outraged by them? Hundreds of animals stuffed into small cages for most of their lives, until they're grown enough and fat enough to make a good meal? Is this natural? No, it's disgusting and wrong. Is it wrong just because people are doing it? No, it's wrong because it's a distortion, a perversion of what those animals are and what they are alive for.
Likewise, when speaking of spiritual entities, angels or demons, we can speak in terms of good and evil. Not that demons and angels are evil and good, per se, but rather that their actions are either evil or good. Demons do not act within the design or structure of their nature, what they are and why they are. Whereas, angels on the other hand do.
As well, when speaking concerning humans, which are a union of the physical and spiritual, we may also speak in terms of good and evil. It is not unknown that the physical laws and spiritual laws or not identical. A spirit is an unextended, indestructible entity, whereas a body is an extended, destructable entity. Hence, the human nature is a complex one, and the line between good and evil is not always clear. That is, the line between acting, or being according to what you are, who you are, and why you are is not always easy to discern. However, rest assured, there is a nature that can be distorted or perverted, and hence we can act in evil ways. That is to say, we can act contrary to our nature, in ways that are destructive to our nature.
Often Christians are accused of making nature seem evil, or calling that which is natural evil. This comes out of a misunderstanding. Because there are both spiritual laws and physical laws encompassed within the human being, there are also aspects of both the physical nature and the spiritual nature encompassed within the human being. For example, human nature encompasses such needs or desires as to feed, or to reproduce, or to survive, or even to change. Human nature also encompasses such needs or desires as to celebrate, or to grieve, or to practice self-discipline, or to liberate, or practice freedom, or even to simply remain unchanged. Since the nature of human beings is not perfect (due to sin, which, being an action that negates, or removes from, or destroys nature, altered it, made it less than it was) humans do not have perfect self-control (as they would if their natures were perfect). This is a significant issue, since to be human is to bear the image and likeness of God, which entails free will and intellect. Since we no longer have perfect self-control, we no longer have perfect free will. It is in denying, or mastering the physical or ourselves that we enhance, or practice and strengthen our self-control, or self-mastery. This doesn't mean that the natural is evil. And yet, because of the teachings or practices that we employ, the misunderstanding comes about that we believe the natural to be evil. That simply is not the case. The natural is good, it is that which destroys the natural that is evil.